1. Field of the Invention
The present invention relates to the field of Internet working protocols (IP), and more particularly, the present invention relates to a mobile networking system which permits the tracking and location of mobile hosts (MH) utilizing an Internet protocol.
2. Art Background
Historically, computers coupled to a network were located at fixed positions on the network and not easily moved to new locations. The relocation of a fixed host computer required shutting the host system down and physically moving the system to another location on the network. The relocated host computer was then rebooted and reconfigured for its new network location. The advent of portable computers with the power of traditional desktop workstations has made it possible to easily relocate the host portables from one network to another. However, the ease of movement of the portable machine across networks has resulted in problems in tracking and locating the mobile machine over the networks. For example, if a user of a portable laptop workstation carries his machine from a network in Palo Alto, Calif. to Bangkok, Thailand, the network in Bangkok must be made aware that the mobile host is now coupled to its network, and the Palo Alto network must also be programmed to send any messages ("IP packets") intended for the mobile host to the Bangkok network.
A number of proposals have been made to add mobile IP nodes to existing fixed node IP networks (See for example, John Ioannidis, Dan Duchamp, Gerald Q. Maguire, Jr., "IP-based Protocols For Mobile Internetworking", Proceedings of the SIGCOMM'91 Conference: Communication Architectures & Protocols, pp. 235-245, ACM, September 1991 (herein referred to as the "Columbia" scheme); Fumio Teraoka, Yasuhiko Yokote, Mario Tokoro, "A Network Architecture Providing Host Migration Transparency", Proceedings of the SIGCOMM'91 Conference: Communication Architectures and Protocols, pp. 209-220, ACM, September 1991 (herein referred to as "Teraoka"); C. Perkins, Yakov Rekhter, "Use Of IP Loose Source Routing For Mobile Hosts", Draft RFC (herein referred to as "Perkins").
The "Columbia" scheme is based on IP-in-IP encapsulation concept ("tunneling") which avoids the problems related to IP options (See for example, Teraoka and Perkins). The Columbia scheme works efficiently for small campus environments and intra-campus mobility. However, as will be described, Columbia reverts to highly sub-optimal routes in case of inter-campus mobility. The present invention discloses methods by which the Columbia scheme can be extended to provide more optimal routes in case of inter-campus mobility, which is redefined herein to mean "wide-area" mobility.
The present invention is inspired by hierarchical fixed node routing, as defined in OSPF. (See for example, J. Moy, "OSPF Version 2", Internet RFC 1248, July, 1991.) One difference between the present invention and hierarchical schemes employed for fixed-node routing (such as OSPF) is that mobility route update information is not flooded on unnecessary routes. Rather, in accordance with the present invention, mobility route update information is back-propagated on active communication paths. This serves to minimize the load on the network due to control information. A two-level tunneling scheme is employed by the present invention to deliver IP packets to the wide-area mobile host. By envisioning special mobility support functionality in routing entities at the boundaries of the hierarchy, much more efficient routes are achieved to wide-area mobile nodes.
In the Columbia scheme, special routers, termed Mobility Support Routers (MSRs) manage the tracking of mobile nodes and provide for the delivery of IP packets to these mobile nodes. Mobile nodes reside on special IP "subnets", such that data packets intended for that subnet end up being routed through an MSR. (MSRs advertise themselves to the networks as being directly attached to this special "subnet"). When an MSR receives a packet for a mobile node whose location it does not know, it multicasts out a WHO.sub.-- HAS request to all MSRs in its campus. (The term "campus" is not well defined from a routing perspective in the Columbia scheme. By default, it is the set of MSRs that cooperate in a certain manner.) A mobile node is always attached directly through one of the MSRs in the network. When this MSR receives the WHO.sub.-- HAS request, it responds with an I.sub.-- HAVE packet, stating in effect that it is serving that MH. The requesting MSR, upon learning of the present location of the MH, encapsulates IP packets intended for the MH within IP packets intended for the responding MSR. This MSR then decapsulates the packets and directly delivers them to the MH, since it is directly attached to the MH, in case the MH is still within its Home campus network.
Moreover, in the Columbia scheme, in case of inter-campus mobility (called a POPUP scenario), a specially designated MSR in the MH's Home Area serves to capture packets intended for that MH. All packets intended for that MH from other campuses and even from the campus where the MH is presently in, are routed through the designated MSR. It has been found that this aspect of the Columbia scheme can lead to highly sub-optimal routes. Assume for example that a Stationary Host (SH device) desires to send IP data packets to an MH which has roamed to a subnet one subnetwork ("hop") away from this SH, and the MH's Home campus is across the country. Packets intended for this MH will be sent to the MH's Home campus network and tunneled back across the country to the campus where the MH is located. This process results in two cross-country packet traversals, where the ideal route is just one hop in length and does not require using a wide-area link.
As will be described, the present invention provides a method for intra-domain tunneling in a mobile IP scheme which is more efficient than the Columbia or other prior systems.